FBI Director James Comey confirmed for the first time Monday that the agency is investigating Russian interference in last year's presidential election and notably Moscow's possible collusion with President Donald Trump's campaign.

He also rejected Trump's claim that predecessor Barack Obama wiretapped his Trump Tower in New York, saying both the Federal Bureau of Investigation and the Justice Department had no evidence to support such allegations.

The explosive testimony in the House Intelligence Committee -- the first public hearing into both controversies -- came as Trump sought to steer the news focus by calling the Russia issue, which has been a cloud over his November victory, "fake news."

His angry tweets added to the huge political pressure from both parties on Comey and Admiral Mike Rogers, the director of the National Security Agency.

But the FBI director opened the hearing with a bombshell -- confirming longstanding reports that his agency is conducting a counterintelligence probe into the Russian government's covert effort to steer the 2016 presidential vote.

"And that includes investigating the nature of any links between individuals associated with the Trump campaign and the Russian government, and whether there was any coordination between the campaign and Russia's efforts," he said.

Comey dated the probe back to July 2016, when the government became aware that Democratic party computers and communications had been broken into by Russia-linked hackers.

Documents stolen in that break-in were released in the final weeks of the campaign to embarrass Democratic candidate Hillary Clinton, who was the front-runner going into the November 8 vote.

"Putin hated Secretary Clinton so much that the flip side of that coin was he had a clear preference to the person running against the person he hated so much," Comey said.

"They wanted to hurt our democracy, hurt her, help him. I think, all three, we were confident in at least as early as December," he said.

Still, Comey and Rogers declined to comment on whether the probe had found that contacts between Trump aides and advisors and Russian officials during the campaign amounted to collusion, citing the need to protect an ongoing investigation.

Ahead of the hearing, Trump tweeted that former intelligence chief "James Clapper and others stated that there is no evidence Potus colluded with Russia."

"This story is FAKE NEWS and everyone knows it!"

The White House said that position supported their view that the Russian issue is being overplayed by Democrats and the media.

As Comey was testifying, a senior administration official said in a written statement: "There is NO EVIDENCE of Trump-Russia collusion and there is NO EVIDENCE of a Trump-Russia scandal."

But officials soundly repudiated the allegation Trump made earlier this month that his predecessor Barack Obama had wiretapped his Manhattan base of operations and residence, Trump Tower.

"With respect to the president's tweets about alleged wiretapping directed at him by the prior administration, I have no information that supports those tweets," Comey told a public hearing by the House Intelligence Committee.

"The Department of Justice has asked me to share with you that the answer is the same for the Department of Justice and all its components. The department has no information that supports those tweets."

It was the first time Comey or the department commented publicly on the claim that Trump continued to repeat throughout last week, without offering any evidence.

Monday's hearing made clear the question of Russian interference in the election will continue to trouble the Trump administration.

Both the House and Senate Intelligence Committees will have more public hearings in the coming weeks, as well as closed-door sessions with Comey, Rogers and other intelligence chiefs to discuss classified information on the probes.

The judiciary committees of both houses are also conducting probes.

But Democrats have expressed concerns that the White House and Republicans would like to stifle the issue, and are calling for an independent probe.

"I believe that we would benefit from the work of an independent commission that can devote the staff and resources to this investigation that we do not have, and that can be completely removed from any political considerations," said Adam Schiff, the senior Democrat on the House Intelligence Committee.